Subroutines don't "send", they "return".
When you say "input", you seem to mean "argument".
Please learn the terminology. It'll help make your posts understandable.

in &testmode the &makeitbig is not returning anything is expecting a value to process

No, not nothing. It's returning the value in $default_value. Did you forget to assign something meaningful to $default_value?

In reply to Re: Subroutine's output as input to a subroutine by ikegami
in thread Subroutine's output as input to a subroutine by props

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